THE COTTON-TOP TAMARIN CARRIES AN EXTENDED SEMENOGELIN-I GENE BUT NO SEMENOGELIN-II GENE

Previous studies have shown that the predominant proteins secreted by the seminal vesicles are transglutaminase substrates which have underg one major structural alterations during evolution. In man, they are kn own as semenogelin I and II; recently it was shown that, similar to ma n, several new world and old world monkeys carry two semenogelin genes as well, the exception being the cotton-top tamarin (Saguinus oedipus ) with a single gene. This gene has now been cloned and identified as a semenogelin I gene, because of a higher number of conserved nucleoti des in the human semenogelin I gene (89 %) than in the human and the r hesus monkey semenogelin II genes (82 %). Furthermore, the difference in sequence similarity indicates that the semenogelin II gene was dele ted from the genome of a progenitor to the cotton-top tamarin after th e duplication that yielded the two semenogelin genes seen in man. Like several other genes expressing seminal-vesicle-secreted transglutamin ase substrates, the cotton-top tamarin semenogelin I gene consists of three exons of 97, 1816 and 146 bp. It codes for a signal peptide of 2 3 amino acid residues and the secreted protein of 592 amino acid resid ues. The molecular mass of 66 kDa is 32% larger than that of the human counterpart and, contrary to human semenogelin I, the cotton-top tama rin protein has the potential to be highly glycosylated as there are 1 4 sites with the consensus sequence for N-linked glycosylation. Approx imately half of the primary structure consists of five nearly identica l tandem repeats of 58 amino acid residues, that probably evolved rela tively late.